MECOPTERA (Mickoleit, 1974)

Sinclair, Bradley J., Borkent, Art & Wood, D. Monty, 2007, The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance, Zoological Journal of the Linnean Society 150 (4), pp. 711-742 : 714-715

MECOPTERA

Description ( Fig. 1A, B )

Testis: The general shape is similar in most genera, comprised of three to four longitudinal follicles fused medially into a single fusiform gland ( Potter, 1938). The only known exception is Boreus Latreille , where two spherical lobes or two sets of five spherical lobes are fused medially ( Potter, 1938; Cooper, 1940). The testis of Nannochorista Tillyard is also fusiform or spindle-shaped, similar to that of most other Mecoptera . Due to the age of the material at hand, no inner divisions could be detected.

Epididymis: Long, inflated, coiled tubes at the base of the testes are present in all genera, except Boreus

( Potter, 1938). In Boreus , the testicular lobes empty into a thin-walled chamber ( Cooper, 1940).

Vas deferens: In Mecoptera , each of the paired vasa deferentia extends posteriorly from the epididymis, bending back anteriorly before joining one another, then entering a pair of large glands. In Nannochoristidae , the two short vasa deferentia join medially just prior to entering the apex of a paired gland. In Boreus , the vasa deferentia curve slightly anteriorly before entering the most posterior of the three anterior lobes of the accessory gland ( Cooper, 1940).

Accessory gland and seminal vesicle: In Panorpa ( Fig. 1A ), at the termination of each of the vasa deferentia is a large, often elongate, paired gland, closely approximated or fused medially ( Potter, 1938; Grell, 1942; Matsuda, 1976). This gland is here referred to as the accessory gland, due to its thick walls and secretory cells ( Grell, 1942). Spermatozoa are stored in the epididymis and no seminal vesicle is present. Often there is a pair of lobes or appendices of various lengths arising on the anterior end or laterally on this large gland, also of similar histology to the main gland ( Grell, 1942). In Nannochoristidae , the accessory glands are joined medially, forming a heart-shaped gland. No internal divisions were visible (but the specimen was quite old), except for a flattened appendix anterodorsally ( Fig. 1B , shaded areas). The accessory gland of Boreus differs from all other Mecoptera in comprising three closely positioned anterior lobes and a more distantly separated posterior lobe ( Cooper, 1940).

Ejaculatory duct: Paired ducts arise from the posterior end of each of the accessory glands and join medially, but remain separate throughout their length and terminate in paired ejaculatory sacs. In Nannochoristidae , the slender, paired ducts are slightly shorter than the accessory gland. Prior to entering the ejaculatory sacs, the ducts are separated by the median depressor muscle of the piston ( Grell, 1942; Hünefeld & Beutel, 2005). In Mecopteran studies ( Potter, 1938; Grell, 1942; Hünefeld & Beutel, 2005) these ducts were labelled vasa deferentia, but we follow Matsuda (1976) in identifying ducts posterior to the accessory glands or exiting the seminal vesicle as ejaculatory ducts.

Ejaculatory apodeme, sperm pump, and aedeagus: The ejaculatory apodeme of Mecoptera functions as a piston, drawn in and out of the chamber ( Willmann, 1981, 1987). The sperm pump (represented by the piston, not shown in Fig. 1A ) is present in most families except Boreidae ( Mickoleit, 1974) and Nannochoristidae ( Willmann, 1981) . In Boreidae , the reproductive tract is modified ( Potter, 1938: fig. 30) and a preformed, two-chambered spermatophore is produced, but is not present in other Mecoptera ( Mickoleit, 1974) . The aedeagus lies in a genital cavity with a pair of lateral plates, which unite medially to form the sclerotized median piece ( Matsuda, 1976). The opening of the sperm pump is narrow and lies on the distal end of the median piece.

Remarks: The accessory glands of Mecoptera have been termed seminal vesicles in the literature (e.g. Miyake, 1913; Potter, 1938; Grell, 1942; Matsuda, 1976), and sometimes only the small appendices have been referred to as accessory glands. We refer to the entire gland as the accessory gland due to its histology (i.e. the presence of large secretory cells) and due to the fact that no spermatozoa are stored in this gland, and thus cannot be termed the seminal vesicle (see Table 3). Mickoleit (1974) and Willman (1987) considered the spermatophore of Boreidae to be independently derived within Mecoptera and not a ground plan condition in this order.

Hünefeld & Beutel (2005) considered the sperm pump of Mecoptera to differ distinctly from the dipteran type. The genital segment, segment 9, is formed chiefly from the dorsomedially and ventromedially fused basal segments of the gonocoxites. The sperm pump is derived within this genital field ( Hünefeld & Beutel, 2005). In contrast, the dipteran sperm pump is formed by a modified endophallus ( Hünefeld & Beutel, 2005).

The male genital tract of Nannochorista , here described and illustrated for the first time ( Fig. 1B ), is similar to that of other Mecoptera illustrated in the survey by Potter (1938), although shorter and stouter. The paired accessory glands are not divided into separate chambers in Mecoptera ( Grell, 1942) .

The Nannochoristidae are often considered the most primitive lineage of the Mecoptera (Willman, 1987) or possibly the sister group to Siphonaptera + Diptera ( Wood & Borkent, 1989) . Recent molecular studies using multiple genes have assigned the Nannochoristidae as the sister group to Siphonaptera + Boreidae ( Whiting, 2002) . There is independent morphological evidence in the form of the structure of ovarioles (paniostic, initial stages of oogenesis completed postembryonically, multiple nucleoli in oocytes, etc.) that support this assemblage (see Simiczyjew, 2002; Grimaldi & Engel, 2005; Beutel & Pohl, 2006). Further analysis of the relationships of Mecoptera to other taxa is provided below in the Discussion.

Figures

Figure 1. Male internal reproductive organs (dorsal view). A, Panorpa (Mecoptera), left testis removed [modified from Grell (1942)]. B, Nannochorista (Mecoptera), left testis removed, shaded areas mark discoloured regions (scale bar = 0.1 mm). C, Spilopsyllus (Siphonaptera), with ventral surface of accessory gland on right [modified from Mead-Briggs (1962)]. D, Xenos (Strepsiptera) [modified from Carcupino et al. (1995)]. acc gl, accessory gland; acc gl app, accessory gland appendix; ej dt, ejaculatory duct; epid, epididymis; p ej dt, proximal ejaculatory duct; sem ves, seminal vesicle; tes, testis; vas df, vas deferens.